The hydroformylation of ethylenically unsaturated compounds to form aldehydes and/or alcohols, is of considerable industrial importance. The process has been in commercial operation for decades and over the years much development work has been done to optimize the reaction conditions, the catalyst system and the equipment. Although significant progress as regards higher yield and selectivity to the desired reaction products has been made, it is felt that in some aspects further improvement of the process is still needed.
Conventional modes of operation were initially based on the use of a cobalt carbonyl catalyst. The activity of this catalyst is relatively low and moreover, when using internal olefins as starting material, a mixture of hydroformylation products is formed containing substantial amounts of branched compounds. For many applications, the presence of these branched compounds is undesirable. Moreover, in view of biological degradability, it is also considered advantageous to produce mixtures exhibiting high linear/branching ratios.
The formation of branched products can be suppressed by using a cobalt-phosphine complex as catalyst. However, at the relatively high reaction temperatures required for an adequate activity of this catalyst system, substantial amounts of saturated hydrocarbons are formed in addition to the desired hydroformylation products.
It has been proposed to use a rhodium-based catalyst for hydroformylation reactions. A limitation of this catalyst consists in that with internal olefins as the starting material, branched products are formed. In general, with a rhodium catalyst, the obtained hydroformylation product predominantly consists of aldehydes. For some uses, e.g. for applications in the detergent industry, alcohols are a preferred starting material. Attempts have therefore been made to enhance the formation of alcohols, rather than that of aldehydes e.g. by increasing the hydrogen/carbon monoxide ratio, but these modes of operation invariably result in the formation of substantial amounts of saturated hydrocarbons.
It would hence be attractive if reaction conditions could be selected and a catalyst could be found such that the production of these saturated compounds is minimized.
In EP 220767, a hydroformylation process is described wherein an alkenically unsaturated compound having at least 5 carbon atoms per molecule is contacted with carbon monoxide and hydrogen in the presence of an aprotic solvent and a catalyst, based on palladium, platinum or a compound of one of these metals, an anion of a carboxylic acid with a pKa of less than 2 and a bidentate of the formula Q.sup.1 Q.sup.2 MQMQ.sup.3 Q.sup.4 wherein M represents phosphorus, arsenic or antimony, Q represents a divalent organic bridging group having at least three carbon atoms in the bridge and Q.sup.1 . . . Q.sup.4 are similar or dissimilar optionally substituted hydrocarbyl groups.
From the experimental results revealed in the examples, it can be seen that under the selected reaction conditions, the conversion is about 65%, the amount of linear compounds in the product mixture is 67% and that, although predominantly aldehydes are obtained, some formation of paraffins also takes place.
EP 495547 relates to a variety of carbonylation reactions, e.g. for the preparation of ketones, esters, aldehydes and alcohols. The hydroformylation of ethylenically unsaturated compounds is also encompassed and illustrated by a number of working examples. According to one of these examples, an alpha-olefin (1-octene) may be hydroformylated at 90.degree. C., using a catalyst, comprising palladium, 1,3-bis(diisopropylphosphino)propane and a sulfonic acid to form aldehydes (and some alcohols) with a linearity of about 85%, the conversion being about 67%. For the hydroformylation of internal olefins, this catalyst is significantly less active.
It has now been found that by selecting a catalyst based on a metal of the platinum group and on a bidentate ligand comprising at least one bivalent cyclic moiety, improved hydroformylation results are achieved as regards, inter alia, conversion rate, linearity of product and suppression of paraffin make.